Engineering thermoplastic plastics are widely used in automotive, electric/electronic, and industrial applications due to high strength, high stiffness, and high heat stability. Particular applications in the automotive markets require moldable thermoplastics that have the mechanical properties and heat stability comparable to metals, high thermal conductivity, and good moisture stability. Providing high thermal conductivity in thermoplastic compositions typically requires high loading of thermally conducting fillers. Unfortunately high levels of fillers often lead to high viscosity compositions that are difficult to mold, especially were fine details are required. Conventional viscosity modifiers such as organic acids, and low viscosity resins, such as polyamide 6,6, are known to reduce melt viscosity when used as additives. However, these materials also lead to undesirable decreases in moisture resistance and physical properties.
Hyperbranched polymers have been disclosed as viscosity modifiers for thermoplastic resins. European Patent 0902803, for instance discloses hyperbranched polyesters. Although these hyperbranched polyesters exhibit good thermal stability in thermo-gravimetric analysis (TGA) alone; in thermoplastic compositions including high melting (≧280° C.) semiaromatic polyamides, and thermally conducting fillers, thermal stability is surprisingly lacking.
Needed are molding compositions having high flow (low viscosity) and high thermal stability at processing temperatures ≧280° C., that exhibit high thermal conductivity and good heat and moisture resistance in molded parts.